This invention relates to an arrangement for open-end friction spinning of the type having two friction rollers that are arranged next to one another to form a wedge-shaped gap serving as a yarn-forming zone. The friction rollers are drivable in the same rotational direction. A fiber feeding duct is aimed at the wedge-shaped gap and forms a scatter zone for the feeding of individual fibers. A suction device generates an air current aimed into the wedge-shaped gap in the area of the scatter zone, and a withdrawal device is provided for withdrawing the yarn, the yarn formation starting at a yarn tip at the end thereof opposite the withdrawal direction.
In the case of a known arrangement for open-end friction spinning disclosed in German Unexamined Published Patent Application (DE-OS) No. 29 43 063, one of the two rollers is formed as a so-called suction roller. It has a perforated shell surface within which a suction insert is arranged that is aimed at the wedge-shaped gap by means of a suction slot, said suction insert being connected to a vacuum source. The second roller, on the other hand, has a closed shell surface. A fiber feeding duct aimed at the wedge-shaped gap at an acute angle is equipped with a duct end piece extending in the direction of the wedge-shaped gap in the area in front of its mouth, this duct end piece being connected to an additional suction device. A conveying air current transporting the individual fibers to the wedge-shaped gap is generated inside the fiber feeding duct essentially via the suction of the suction insert passing through the perforated shell surfaces of one of the rollers. The additional air current directly in front of the mouth has the purpose of causing at least some of the conveyed fibers to change the direction of their motion so that the depositing and tieing of the fibers is improved. This additional air current, which is not directed at the area of the forming yarn, has to be proportioned very carefully so that especially light and short fibers are not sucked off. In order to keep the additional air current away from the direct area of the mouth and the area of the wedge-shaped gap, a baffle plate is provided between the additional suction device and the wedge-shaped gap.
The known arrangement as well as other known arrangements which are not provided with an additional suction device have the disadvantage that the yarn, which forms by means of a yarn tip located opposite the withdrawal device, is already very twisted in the area of the yarn tip. This results in a yarn with a hard twisted core and a relatively soft sheath.
The invention is based on the objective of developing an arrangement of the initially mentioned type so that a yarn is obtained that is twisted as evenly as possible, where the twisting of the core of the yarn is not too hard.
This objective is achieved by providing an additional suction device that generates an air current affecting the yarn tip against the withdrawal direction of the yarn.
By means of this development, an air current component is generated in the area of the yarn tip by means of which the air current component aimed into the wedge-shaped gap and caused by the suction device is reduced. Thus the friction effect in the area of the yarn tip is reduced so that in this area the twisting of the forming yarn is reduced which will receive an increased twist only downstream of the yarn tip when it has a larger diameter. However, the conveying direction component of the air current is maintained up to almost directly the wedge-shaped gap so that a sufficient amount of fibers will also reach this area of the forming yarn tip.
In a further development of the invention, it is provided that the friction effect in the area of the yarn tip is reduced because of the design of the rollers and/or of the suction device generating the air current aimed into the wedge-shaped gap. This has the effect that to an increased extend an excessive twisting in the area of the yarn tip is avoided, while the air current generated by the additional suction device ensures the transport of the fibers also to this area.
In a further development of the invention, it is provided that a suction nozzle is provided as the additional suction device that is arranged as an extension of the wedge-shaped gap at the end facing away from the withdrawal device. As a result, it is ensured in a simple manner that the additional air current acts precisely as an extension of the yarn tip.
In the case of another preferred embodiment of the invention, it is provided that the additional suction device is arranged at a distance to the area where the yarn tip is formed and is aimed at the wedge-shaped gap approximately radially, and that means are provided for deflecting the air current in the direction of the wedge-shaped gap. In this manner also, an additional air current is generated in the wedge-shaped gap in the area of the yarn tip which is aimed against the withdrawal direction.
The additional suction device, especially when it is aimed at an acute angle with respect to the conveying direction of the fed fibers, also has the advantage that at least some of the conveying air current can be generated by it which then must not be sucked through the perforated shells of the rollers. In the case of a sharp deflection between the conveying air current and the air current taken in by the additional suction device, the fibers do no follow this deflection or follow it only insignificantly so that they continue to fly into the desired areas of the wedge-shaped gap without problems.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, embodiments in accordance with the present invention.